Paul J. Browne, the Police Department’s chief spokesman, said the judge’s decision was “not a setback” because it was consistent with new housing vertical patrol, procedures and training curriculum put in place this year.

Before making a trespass arrest, Mr. Browne said, officers are trained to ask a person: Do you live in the building? Are you visiting someone? Do you have business there? Based on the answers, and on follow-up questions, an officer might establish probable cause for an arrest, or might tell the person to leave or become satisfied that he or she can stay.

“Housing officers are trained that they must establish a reason to approach someone before questioning individuals in a housing development — for example, violations of Housing Authority rules and regulations,” Mr. Browne said. “Furthermore, the judge said the officer in the Ventura case did not adequately establish reasonable suspicion or properly articulate probable cause for a trespassing arrest.”

Mr. Browne said the department’s new guidelines and training grew out of meetings with tenants’ organizations and the city Housing Authority, and did not suggest that officers’ behavior in patrolling public housing prior to the new rules was faulty.

A spokeswoman for Bridget G. Brennan, the special narcotics prosecutor, said the judge’s decision was narrow and “we’re not concerned that it has any precedential value.”

But Steven Banks, attorney-in-chief at the Legal Aid Society, said that what Officer Del Toro “candidly admitted” in his testimony is a “serious daily occurrence.” He said it encapsulated what had led his agency, the NAACP Legal Defense and Education Fund Inc., and a private law firm to file a federal lawsuit against the city.